Anyone who has spent 48 minutes on the phone waiting for a customer service representative can identify with the mounting impatience of the title character in Ken Loach’s scalding cinematic outcry, “I, Daniel Blake.”

That’s how long Daniel, a 59-year-old widowed carpenter recovering from a heart attack, waits to connect with a government representative in the first of many infuriating phone calls. Multiply that frustration a hundredfold, and you can imagine the Kafkian nightmare that Daniel endures as he seeks the restoration of his employment and support allowance from the British state after it was mysteriously taken away. Treated with suspicion, hostility and barely disguised contempt by low-level government officials, Daniel is required to supply exhaustive proof of his disability and of his futile job search.

Put simply, he is caught between two interconnected bureaucracies, one medical, the other employment related in an excruciating Catch-22 situation. He can’t work until his doctors give him the O.K.; he has to look for a job when he should be resting. In the meantime, his meager resources are dwindling.

“I, Daniel Blake” is a powerful return to form for Mr. Loach, the much-honored left-wing British filmmaker who is now 80 and is still in full command as a filmmaker and a social critic. (He has the political outlook of a British Michael Moore.)

This bleak film set in Newcastle won the Palme d’Or last spring at the Cannes Film Festival. Its performances — from the comedian Dave Johns, who portrays Daniel, down to the tiniest role — are so fine-tuned that you often feel you are watching a Frederick Wiseman documentary.

While viewing “I, Daniel Blake,” it’s easy to forget that Mr. Loach is a polemicist who has always stood up for working-class Britons, whom his films portray as oppressed, mistreated and noble. He and his longtime screenwriting partner, Paul Laverty, are masters of a dour, clinical neorealism that conveys their feisty resilience in a conservative climate in which struggling workers are demonized as little better than parasitic social refuse.

You may applaud when Daniel finally confronts the government workers in person, but the experience is actually more humiliating than dealing with them by telephone. When one sympathetic social worker gives him an extra moment of time, she is sharply reprimanded by her superior. Interviewed face to face, the poor and indigent are interrogated like naughty school children. If they raise their voices in protest, security guards appear to remove them.

For Daniel, a skillful woodworker, the seemingly insurmountable obstacle in his quest is his complete ignorance of computers. It makes it impossible for him to create an acceptable résumé, which he is required to post online. The digital divide looms as a personal catastrophe as you watch him being shown the basics but finding himself stymied by every small misstep.

What makes the pain of this film bearable is Daniel’s unquenchable decency, courage and perseverance: Mr. Johns, who bears a striking resemblance to the musician Phil Collins, portrays him as a genuine working-class hero with a deep streak of kindness and generosity, a besieged Everyman who reacts to injustice and humiliation with fuming indignation. He refuses to surrender to despair.

Is he too good to be true? Probably.

At the welfare office, he observes a young woman, Katie (Hayley Squires), and her two children being turned away after arriving a few minutes late for an appointment because she took the wrong bus. Daniel takes it upon himself to be her defender, and for his pains is ousted along with Katie and her children.

Katie, we learn, was evicted from her London apartment after filing a complaint. Daniel soon becomes her protector, a creative Mr. Fix-It who makes her crumbling apartment a little less shabby, and a sort of surrogate father to her children. (Fortunately, the movie doesn’t take the Hollywood route of suggesting any romantic connection between the two.) In her quiet way, Katie is as heroic as Daniel. She goes without food to feed her children, is caught shoplifting groceries and in a moment of desperation at a food bank, tears the lid off a can of beans and pours the syrup into her mouth.

“I, Daniel Blake” builds up an oppressively claustrophobic atmosphere of mounting dread, and you wonder if the stresses of Daniel’s circumstances will catch up with him in his weakened state. The movie eventually goes a little too far, and makes Daniel’s predicament a popular rallying cry on the street. It’s a showy feel-good moment in an otherwise feel-bad film.